1. Field of the Invention
The present invention relates to a compound semiconductor device with a two-dimensional carrier gas channel and a production method thereof.
2. Description of the Related Art
A transistor having a hetero junction of compound semiconductors so as to generate a two-dimensional electron gas is known as “high-electron-mobility transistor”, or its shortened form “HEMT”.
Typically a hetero junction in a HEMT is comprised of an AlGaAs layer and a non-doped GaAs layer. Because AlGaAs has a wider band gap than GaAs, a quantum well is formed in the GaAs layer along the hetero junction. Abundant electrons supplied by the AlGaAs layer to the quantum well forms a two-dimensional electron gas and can quickly move therethrough because the non-doped GaAs layer is free from impurities which cause collision with the electrons. The quantum well thus formed is referred to as “two-dimensional electron gas (2DEG) channel”.
Because of such high electron mobility, HEMTs are widely used for producing high-speed switching devices and high-frequency devices. Recently an AlGaN/GaN system is under intense study because an AlGaN layer on a GaN layer generates a relatively dense 2 DEG even if the AlGaN layer is un-doped. HEMTs of the AlGaN/GaN system are considered to be promising in view of efficiency and operation speed.
Japanese Patent Unexamined Publications No. 2006-5005 and 2009-060049 disclose related arts.